The average surface resistance of a pine forest derived from Bowen ratio measurements

1975 ◽  
Vol 8 (3-4) ◽  
pp. 453-464 ◽  
Author(s):  
J. H. C. Gash ◽  
J. B. Stewart
Keyword(s):  
Surface Resistance ◽  
Bowen Ratio ◽  
Pine Forest ◽  
Average Surface

scholarly journals Seasonal and inter annual variability of energy exchange above a boreal Scots pine forest

2010 ◽  
Vol 7 (4) ◽  
pp. 6441-6494 ◽  
Author(s):  
S. Launiainen
Keyword(s):  
Heat Flux ◽  
Scots Pine ◽  
Seasonal Cycle ◽  
Sensible Heat Flux ◽  
Bowen Ratio ◽  
Pine Forest ◽  
Surface Conductance ◽  
Sensible Heat ◽  
Annual Variability ◽  
Scots Pine Forest

Abstract. Twelve-years of eddy-covariance measurements conducted above a boreal Scots pine forest in Hyytiälä, Southern Finland, were analyzed to assess the seasonal and inter-annual variability of surface conductance (gs) and energy partitioning. The gs had distinct annual course, driven by the seasonal cycle of the Scots pine. Low gs (2–3 mm s−1 in April) restricted transpiration in springtime and caused the sensible heat flux to peak in May–June while evapotranspiration takes over later in July–August when gs is typically 5–7 mm s−1. Hence, during normal years Bowen ratio decreases from 4–6 in April to 0.7–0.9 in August. Sensitivity of gs to ambient vapor pressure deficit (D) was relatively constant but the reference value at D=1 kPa varied seasonally and between years. Only two drought episodes when volumetric soil moisture content in upper mineral soil decreased below 0.15 m3 m−3 occurred during the period. Below this threshold value transpiration was strongly reduced, which promoted sensible heat exchange increasing Bowen ratio to 3–4. Annual evapotranspiration varied between 218 and 361 mm and accounted between 50% and 90% of equilibrium evaporation. The forest floor contributed between 16 and 25% of the total evapotranspiration on annual scale. The fraction stayed similar over the observed range of environmental conditions including drought. The inter-annual variability of evapotranspiration could not be linked to any mean climate parameter while the summertime sensible heat flux and net radiation were well explained by global radiation. The energy balance closure varied annually between 0.66 and 0.95 and had a distinct seasonal cycle with worse closure in spring when large proportion of available energy is partitioned into sensible heat.

scholarly journals Effect of land use on carbon dioxide, water vapour and energy exchange over terrestrial ecosystems in Southwestern France during the CERES campaign

2009 ◽  
Vol 6 (2) ◽  
pp. 2755-2784 ◽  
Author(s):  
N. Jarosz ◽  
P. Béziat ◽  
J. M. Bonnefond ◽  
Y. Brunet ◽  
J. C. Calvet ◽  
...  
Keyword(s):  
Sensible Heat Flux ◽  
Bowen Ratio ◽  
Terrestrial Ecosystems ◽  
Bare Soil ◽  
Pine Forest ◽  
Maritime Pine ◽  
The Other ◽  
Mature Forest ◽  
Forest Sites ◽  
Winter Crops

Abstract. Eddy fluxes were measured over different ecosystems, winter and summer crops, a maritime pine forest at different stages of development and grassland, from 17 May to 26 June 2005 in the southwestern region of France. During the experiment, summer crops started growing whereas winter crops and grassland achieved their senescence. Comparatively, the other ecosystems had a much slower growth emphasized by soil water deficit at forest sites. The ten ecosystems showed different partitioning of available energy. Net radiation was the highest above the maritime pine forest, followed, in decreasing order, by the crops, the vineyard and the grassland. Over the whole campaign period, the Bowen ratio (β=H/LE) was larger above the forest sites than for the other sites. The various vegetation types also showed contrasting net ecosystem exchange (NEE) dynamics following their growth status and respective behaviour in response to drought. Both the clearcut and summer crops before irrigation and plant growth behaved as sources of CO2, whereas the vineyard, the mature forest and winter crops acted as sinks. However the maize crops became substantial sinks of CO2 after the start of irrigation and canopy growth, with fluxes twice as large as for the mature pine forest. Finally, throughout the experiment, forest, grassland and crops sequestrated from about 50 gC m−2 to 230 gC m−2, while the cleacut and the beans crop rejected about 30 gC m−2. These results support the idea that converting a mature forest to a clearcut or bare soil available to agricultural use enhances the sensible heat flux and shifts the ecosystem from a sink to a source of carbon.

scholarly journals Responses of energy partitioning and surface resistance to drought in a poplar plantation in northern China

2015 ◽  
Vol 12 (1) ◽  
pp. 345-388 ◽  
Author(s):  
M. Kang ◽  
Z. Zhang ◽  
A. Noormets ◽  
X. Fang ◽  
T. Zha ◽  
...  
Keyword(s):  
Water Use ◽  
Surface Resistance ◽  
Bowen Ratio ◽  
Northern China ◽  
Energy Partitioning ◽  
Ecosystem Functions ◽  
Dominant Factor ◽  
Poplar Plantation ◽  
Limited Region ◽  
Poplar Plantations

Abstract. Poplar (Populus sp.) plantations have been used broadly for combating desertification, urban greening, and paper and wood production in northern China. However, given the high water use by the species and the regional dry environment, the long-term sustainability of these plantations needs to be evaluated. Currently, the understanding of energy partitioning and canopy resistance to water vapor and CO2 in poplar plantations is limited, impeding an accurate assessment of their true ecosystem functions. This study examined the variability of canopy bulk resistance parameters and energy partitioning over a four-year period encompassing both dry and wet conditions in a poplar (Populus euramericana CV. "74 / 76") plantation ecosystem located in northern China. Available energy (Net radiation Rn minus Soil Heat Flux, G) partitioning to latent (LE) and sensible (H) heat was responsive to climatological drought, with LE/(Rn-G) ranging from 62% in wet years (e.g. 2007 and 2008) to 53% in dry years (e.g. 2006 and 2009), and H/(Rn-G) from 25 to 33% between wet and dry years. Correspondingly, the Bowen ratio (β=H/LE) were 0.83 and 1.57. Surface resistance (Rs) had the greatest response to drought (+43%), but the aerodynamic and climatological resistances did not change significantly (p > 0.05). Partial correlation analysis indicated that Rs was the dominant factor in controlling the Bowen ratio. Furthermore, Rs was the major factor controlling LE during the growing season, even in wet years, as indicated by the decoupling coefficient (Ω = 0.45 and 0.39 in wet and dry years, respectively), and the LE / LEeq ratio ranged from 0.81 and 0.68 in wet and dry years, respectively. In general, the dry surface conditions dominated in this poplar plantation ecosystem regardless of soil water availability suggesting that fast-growing and water use-intensive species like poplar plantations are poorly adapted for the water limited region.

scholarly journals Seasonal and inter-annual variability of energy exchange above a boreal Scots pine forest

2010 ◽  
Vol 7 (12) ◽  
pp. 3921-3940 ◽  
Author(s):  
S. Launiainen
Keyword(s):  
Heat Flux ◽  
Scots Pine ◽  
Seasonal Cycle ◽  
Sensible Heat Flux ◽  
Bowen Ratio ◽  
Pine Forest ◽  
Surface Conductance ◽  
Sensible Heat ◽  
Annual Variability ◽  
Scots Pine Forest

Abstract. Twelve-years of eddy-covariance measurements conducted above a boreal Scots pine forest in Hyytiälä, Southern Finland, were analyzed to assess the seasonal and inter-annual variability of surface conductance (gs) and energy partitioning. The gs had distinct annual course, driven by the seasonal cycle of the Scots pine. Low gs (2–3 mm s−1 in April) cause the sensible heat flux to peak in May–June while evapotranspiration takes over later in July–August when gs is typically 5–7 mm s−1. Hence, during normal years Bowen ratio decreases from 4–6 in April to 0.7–0.9 in August. Sensitivity of gs to ambient vapor pressure deficit (D) was relatively constant but the reference value at D = 1 kPa varied seasonally and between years. Only two drought episodes when volumetric soil moisture content in upper mineral soil decreased below 0.15 m3 m−3 occurred during the period. Below this threshold value, transpiration was strongly reduced, which promoted sensible heat exchange increasing Bowen ratio to 3–4. Annual evapotranspiration varied between 218 and 361 mm and accounted between 50% and 90% of equilibrium evaporation. The forest floor contributed between 16 and 25% of the total evapotranspiration on annual scale. The fraction stayed similar over the observed range of environmental conditions including drought periods. The inter-annual variability of evapotranspiration could not be linked to any mean climate variable while the summertime sensible heat flux and net radiation were well explained by global radiation. The energy balance closure varied annually between 0.66 and 0.95 and had a distinct seasonal cycle with worse closure in spring when a large proportion of available energy is partitioned into sensible heat.

scholarly journals Energy partitioning and surface resistance of a poplar plantation in northern China

2015 ◽  
Vol 12 (14) ◽  
pp. 4245-4259 ◽  
Author(s):  
M. Kang ◽  
Z. Zhang ◽  
A. Noormets ◽  
X. Fang ◽  
T. Zha ◽  
...  
Keyword(s):  
Heat Flux ◽  
Surface Resistance ◽  
Sensible Heat Flux ◽  
Bowen Ratio ◽  
Northern China ◽  
Energy Partitioning ◽  
Dominant Factor ◽  
Poplar Plantation ◽  
Area Index ◽  
Limited Region

Abstract. Poplar (Populus sp.) plantations have been, on the one hand, broadly used in northern China for urban greening, combating desertification, as well as for paper and wood production. On the other hand, such plantations have been questioned occasionally for their possible negative impacts on water availability due to the higher water-use nature of poplar trees compared with other tree species in water-limited dryland regions. To further understand the acclimation of poplar species to semiarid environments and to evaluate the potential impacts of these plantations on the broader context of the region's water supply, we examine the variability of bulk resistance parameters and energy partitioning in a poplar (Populus euramericana cv. "74/76") plantation located in northern China over a 4-year period, encompassing both dry and wet conditions. The partitioning of available energy to latent heat flux (LE) decreased from 0.62 to 0.53 under mediated meteorological drought by irrigation applications. A concomitant increase in sensible heat flux (H) resulted in the increase of a Bowen ratio from 0.83 to 1.57. Partial correlation analysis indicated that surface resistance (Rs) normalized by leaf area index (LAI; Rs:LAI) increased by 50 % under drought conditions and was the dominant factor controlling the Bowen ratio. Furthermore, Rs was the main factor controlling LE during the growing season, even in wet years, as indicated by the decoupling coefficient (Ω = 0.45 and 0.39 in wet and dry years, respectively). Rs was also a major regulator of the LE / LEeq ratio, which decreased from 0.81 in wet years to 0.68 in dry years. All physiological and bioclimatological metrics indicated that the water demands of the poplar plantation were greater than the amount available through precipitation, highlighting the poor match of a water-intensive species like poplar for this water-limited region.

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